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Pernicious Anaemia Society
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Advice on Second B12 Test

So I eventually had my intrinsic factor results back last week – negative. Given all the things I’ve read about the IFAB test I wasn’t particularly surprised, but of course it’s set me worrying about not getting the treatment I need i.e. no injections. I went to see my GP this morning, and she’s told me the low B12 must be down to my diet and to eat more oily fish. I pushed the issue and asked, if it is in fact my diet and I make a change in that respect, are they going to retest my B12 to see if the levels return to normal? She has agreed to another blood test at the end of this month.

I don’t really believe it’s my diet – I already eat plenty of meat, fish and dairy products, but of course I will still see if I can make any changes and maybe start taking a supplement. However, I just wondered, given I’ve already had the 6 loading doses, is this going to massively skew the results? I had my last injection on 18th December, and my blood test is 23rd February. Obviously I know they usually advocate an injection every 3 months, so presumably this is how long they think it lasts in your system, but I also know it’s different for every person, and some people self medicate on a far more regular basis. Does anyone have any thoughts? Is it still worth going for the test?

I also asked for a copy of my original test results from my blood test back in October:

Serum vitamin B12 – 110 ng/L (145 - 910)

Serum folate – 4.6 ug/L (3.0 – 20.0)

I don’t really know what to make of these yet. Can anyone comment? The folate seems within range, but at the very low end, so should I be thinking of taking a supplement for that as well? My symptoms are extreme fatigue, occasional shortness of breath, dry skin & nails, sleep problems, mouth ulcers, digestive issues and brain fogs. I’m very new to all this and still making sense of everything I’ve read, so any advice would be gratefully received. Many thanks.

PS: As an amusing aside – having chased my IF results for over 8 weeks, it was quite funny when I finally said it was getting silly and could they follow them up. Receptionist suddenly located them on the system within 2 minutes. The awkward silence when she did (having told me they can take months to come back) was rather funny. I put it down to the fact she could see they’d obviously come back weeks ago. Funnily enough, having obtained a hard copy this morning, it’s stamped “Received 13th December” – just 9 days after my test. Awesome.

10 Replies

Hi Fierybiscuits two months between injections and re-test may not be enough - unless the result comes back low.

Were you supplementing with folic acid whilst having the B12 injections?

You could always ask for an MMA test. Methylmalonic acid is a chemical used up in one of the cellular reactions mediated by B12. If there's not enough B12 in the cell then MMA levels will rise. If they're not high then it means your cellular levels of B12 are OK. High levels of plasma MMA (>0.75umol/L0 almost invariably indicate cobamalin deficiency

I am not a medically trained person but I've had P.A. (a form of B12 deficiency) for more than 45 years.

I wish you well

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Hi Clive.

Thanks for your reply. I’ve never taken any B12 or Folate supplements before. My doctor sent me for blood tests in October as I was feeling exhausted and had some digestive problems. She assumed IBS and was just ruling things out, but the tests came back indicating low B12, which had also shown on another blood test about a year previous (although nobody had ever told me about it). I was sent for the IFAB test and the loading doses in early December.

It was difficult to tell how I felt after the loading doses as I came down with a fairly dreadful cold at the same time - I think I felt a little perkier for a while, but I’m back to feeling incredibly lethargic again (I keep falling asleep at my desk and find it very difficult to concentrate). IFAB has since come back negative, so I’m not sure what to think as to the cause of the deficiency. Doctor says diet, but I’m not vegan or vegetarian (which I believe is the main dietary culprit), and I eat a relatively balanced diet. My great grandmother apparently suffered with PA so, although not a very close relative, I believe it can run in families.

I’m now worrying that I have PA but because of the negative test (which I’ve seen can be quite unreliable), I won’t ever be treated with injections, but that supplements will do nothing (although I'm going to try and see). I’m only 32 and frightened of symptoms getting worse and/or developing neurological problems. I suppose I'll have to wait and see about the blood test, but then if the level has gone up I'm not going to know whether it's down to a change of diet/ adding supplements or the effect of the loading doses 2 months previously. I’ve never heard of the MMA test, so it’s certainly something I’ll investigate. Thank you.


yes get a MMA and homocysteine test to determine accurate B12 levles. Just a B12 serum blood test can be very inaccurate and not show the true deficiency. it's like a random glucose shows you might have a high blood sugar but a hemoglobin A1c shows the accurate levels of glucose same with B12, the blood tests may show a low level, but MMA and homocysteine levels show the accurate level which could be much worse than the B12 blood test shows.

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write to your GP telling them to read the BCSH guidelines on diagnosis and treatment of cobalamin and folate disorders which they can access through the BNF but can also be accessed here


key points that they need to take on board are

a) there are a large number of absorption problems that can cause B12 deficiency - it isn't a question of PA or diet.

b) the IFAB test is notoriously prone to false negatives 40-60% of the time depending on the assay method. This means that, whilst it is a good test for demonstrating that someone does have PA it is not a test that can be used to rule out PA as the cause of deficiency.

The guidelines recognise this by listing among causes IFAB negative PA

In terms of the testing: The chances are that your tests will come back very high in February. This cannot be used to rule out PA as they have filled your body up with a huge amount of B12 by giving you an injection. This can stay in the blood for a very long period of time. The test will only be significant if it comes back low.

Serum B12 only measures the amounts of B12 in your blood - it doesn't tell your GP anything about what is now happening at the cell level and the introduction of huge amounts of B12 into your blood stream means that the normal range really doesn't apply after loading shots.

Significant numbers of people respond to high levels of B12 in serum by making the mechanism that allows transfer from blood to cells a lot less efficient leading to a 'functional B12 deficiency - a recognised consequence/symptom of some conditions that will cause serum B12 to be elevated without supplementation of any form

Personally I think the test will be a waste of time and money.

Problems that affect B12 absorption can also affect the absorption of other vitamins and minerals - notably folate and iron. If your diet is rich in sources of folate then the results may be evidence of impaired folate absorption.

Your need for folate can increase when your B12 levels have been treated through the loading shots - as many of the processes that use B12 also use folate so it's possible that you may become folate deficient when you start treatment

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Hi again everyone,

I’ve read a lot of the information that was recommended (the BSH guidelines in particular), but am still a bit confused. From the flowchart (and despite my IFAB test coming back negative), my serum B12 results (110ng/L) should have warranted a diagnosis of Antibody Negative Pernicious Anaemia (but only if a “clinical response” is present following treatment). The second flowchart, for those without “clinical parameters,” still reaches the same diagnosis for someone with my B12 level (“further investigation and management as in algorithm 1”). Should I be pushing my GP to accept that diagnosis and continue treatment, or asking for the MMA/Homocysteine tests first? And if the latter, would the loading doses I had in December affect those?

I don’t really know whether I had “clinical parameters” or not. I went to the GP just with the extreme tiredness and gastric issues – it’s only on researching B12 that I’ve realised other things (such as dry skin/nails, sleep & concentration problems, mood swings, mouth ulcers etc.) could be a result of it. I’ve had a very patchy (but not particularly swollen) tongue a few times, so I don’t know whether this is a sign of glossitis, but I’ve certainly never bothered to mention it to the doctor, so I suppose I’m worried my doctor will think I’m imagining symptoms to fit the diagnosis. I’d always just put these things down to being tired and/or run down.

I didn’t notice a huge improvement following my loading doses but, as I mentioned before, I was poorly just after having them so it was hard to tell, and I’ve gone back to feeling exhausted again. I don’t know what to put that down to – whether something beyond the B12 is at work, whether I didn’t feel the effects because I was ill, or whether they’ve worn off quickly (I know some people feel they need a lot more than the 3 monthly injections). Perhaps I should push for the extra tests for a more definitive answer, but would I need to wait for the loading doses to leave my system and, if so, any idea how long?

PS: I’m going to cancel that second B12 test as it sounds like it’ll be a waste of time, but I’ve booked another GP appointment at the end of this month, so am just trying to understand from what angle I need to approach it. My anxiety is already going haywire! Many thanks 😊


MMA and homocysteine unlikely to be useful now - really need to be done before loading doses. B12 deficiency develops over a long period of time - years or even decades so, whilst it is possible that there may be other factors involved I'd suggest keeping them on you list of symptoms and monitoring them.

I think your best bet is to try and get your GP to recognise that, even if the IFA test has come back negative - the fact that your deficiency wasn't dietary - means that you have some sort of absorption problem.

Ask them to test for H pylori infection and rule out other possible absorption problems - like coeliacs. H pylori is treatable - so you might not need further injections - but most other absorption problems aren't curable which means injections for life - and is one reason why the guidelines don't go for constant checking of B12 levels as a guide to treatment.

The anxiety may be an indication that you now need to keep your B12 levels really high - my anxiety levels went through the roof after I started treatment and stayed there until I figured out that I actually now need a lot more B12 than I was being given. I found that a nasal spray worked very well for me - but you may want to try sublinguals or high dose oral - it can be effective but there is no guarantee.

Your GP may raise red herrings about overdosing on B12 (hysterical laughter - the treatment for cyanide poisoning is 5000x the amount you are getting in a shot administered intravenously over 15 minutes with a follow on dose 30 minutes later if needed ... and the danger there is hypertension from the amount of fluid being injected - no toxicity).

Suggest that you see how the appointment goes. It may be useful to make notes and have a script before you go in and you may find it useful to take a friend with you - particularly if you are having problems with anxiety - it can help with communications to have another pair of ears with you.

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Thanks so much for your advice. Certainly feel a lot more prepared going to see my doctor now :)

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Some links that may be of use

"I don’t really believe it’s my diet"

Risk factors for P and B12 deficiency




Coeliac Disease

NICE guidelines Coeliac disease (2015 version) suggests anyone with unexplained B12 deficiency, folate deficiency or iron deficiency should have tests for Coeliac disease.



B12 Deficiency Symptoms

pernicious-anaemia-society.... I ticked all my symptoms on PAS checklist and gave a copy to my GPs.


b12d.org/admin/healthcheck/... (may need to be B12d.org member)

UK B12 documents

BSH Cobalamin and Folate Guidelines


Flowchart from BSH Cobalamin and Folate Guidelines


Flowchart outlines when PA and Antibody Negative PA can be diagnosed in UK. Some UK GPs may not be aware of this document.

BMJ B12 article






B12 books I found useful

"What You Need to Know About Pernicious Anaemia and B12 Deficiency" by Martyn Hooper

Martyn Hooper is the chair of PAS (Pernicious Anaemia Society). Book is up to date with UK b12 guidelines. I gave a copy to my GPs.

"Living with Pernicious Anaemia and Vitamin B12 Deficiency" by Martyn Hooper

Has several case studies.

"Could it Be B12?: An Epidemic of Misdiagnoses" by Sally Pacholok and JJ. Stuart (USA authors)

Very comprehensive with lots of case studies.

PAS (Pernicious Anaemia Society)


PAS tel no +44 (0)1656 769717 answerphone

Link about What to Do Next if B12 deficiency is suspected


Links about blood tests




Full Blood Count

Do you have up to date FBC results? There can be useful clues on FBC as to whether b12, folate or iron deficiency are a possibility.



Folate Deficiency


UK B12 blogs

Martyn Hooper's blog about PA


B12 Deficiency Info blog


I am not medically trained.


sounds like a doctor who doesn't have a clue. Get the book Could it Be B12? by Sally Pacholok and give it to your doc! Seriously I cannot believe how many physicians in this world are clueless about B12 deficiency. Mine included. Also have all of your family members checked. It's not always about diet, it's usually about your parietal cells in your gut no longer able to absorb B12, or it's a medication like Metformin that is causing B12 to not absorb or many other meds that are like that or it's a gene that you have MTHFR I think it is called that is causing it. If you are vegan or have been vegan for several years, you might have depleted your B12 that way too, as there is NO B12 in veggies, only in meat and dairy. Point is you are very deficient and needs injections to get your B12 way up there again. You can't overdose on it either, you pee out excess. But you are in the range where you could have long term neuro problems if it's not corrected so push it with the doc. You can also order B12 liquid form from Amazon or likely in your area somewhere, 3000 mcg daily and B12 patches 1200 mcg, but you likely need injections for at least a while if not permanently. You can do your own injections after a while also if you request it once stable. I hope you feel better. I'm just on the beginning process of this myself. I also feel like total rot every day and wake up feeling like total rot, too many symptoms to count, and can hardly wait til I feel better too. good luck


Many thanks for all your responses. Looks like I have a lot of reading to do 😊


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